In an effort to understand the organizational structure of retrovirus genomes, the nucleotide sequence of the chicken cellular myc gene (c-myc) has been determined and compared to the MC29 (Avian myelocytomatosis virus) v-myc gene. The cellular gene shares 1.6 kilobase homology with viral-specific sequences, interrupted by 972 non-homologous sequence. The interrupting sequence can be identified as a true intervening sequence by the presence of consensus donor and acceptor splice signals. The total number of viral-specific nucleotides in c-myc is identical to the number of v-myc. The protein termination signal which is located within myc-specific sequences, is conserved in c-myc. Cellular and viral genes differ by 15 nucleotides, none generating a new termination codon. In addition, c-myc contains polyadenylation signal and polyA-acceptor signals located in the 3' flanking cellular sequences.